The Role of Modeling & Simulation in the Mitigation of V-22 Tiltrotor Formation Flight Wake-Induced Roll-off

Abstract
A real-time free wake modeling capability developed by Continuum Dynamics, Inc. (CDI) was employed by NAVAIR in the mitigation of the wake-induced roll-off hazard experienced by V-22 tiltrotor aircraft while flying in formation in low-speed conversion mode flight. Sub-scale wind tunnel investigations indicated roll-upsets could exceed the control power of the aircraft. PIV measurements from the wind tunnel tests helped characterize the wake and provided the basis for a limited, steady-heading wake encounter simulation capability; however two roll-off events in 2008 occurring in descending turning flight underscored the need for a dynamic wake model. The wake model adopted was originally developed by CDI under a NASA SBIR program for evaluating wake turbulence hazards between fixed and rotary wing aircraft operating in congested airspace. Tiltrotor specific modifications to CDI’s Multiple Aircraft Simulation Tool (MAST) wake model were made and empirical tuning undertaken to improve correlation with the scaled PIV wake measurements. The enhanced MAST wake model was then implemented in the V-22 simulator at NAVAIR’s Manned Flight Simulator (MFS) and in an off-line analysis tool. Both were employed in NAVAIR’s efforts to mitigate the roll-off hazard, including: characterization of tiltrotor wake with age for establishing NATOPS wake avoidance guidelines, investigation of formation flight roll-off events, development of real-time dynamic wake encounter simulation capability, support of control law design changes for improved lateral control power, development of roll-off recovery procedures, support of V-22 formation flight testing by providing pre-flight test conditions and post-flight encounter assessments, and the eventual implementation of a wake encounter simulation capability in the V-22 trainers.